So I'm looking at the K&N oil filter but read that the o-ring is a tad bigger than factory filter? Can someone shine some light on this subject or give me a recommendation on what filter to use besides factory.  Thanks

[2015 Z Force 800 53/Trail EPS]

The K&N for the CFM 800 does fit fine. HiFlow filters also makes one for the CFM800 I believe. Do not use one for the Rotax 800 as it has a larger seal and may not seal correctly. You are always safe with the OE.

I've been using a K&N-152 without any issues since my machine was new.